Subcutaneous adipose tissue dopamine D2 receptor is increased in prediabetes and T2D

PURPOSE

To evaluate the dopaminergic signaling in human adipose tissue in the context of obesity and type 2 diabetes (T2D) and potential direct implications in adipose tissue metabolism.

METHODS

mRNA and protein expression of dopamine receptors D1 and D2 (DRD1 and DRD2) were determined in subcutaneous adipose tissue from subjects without or with T2D and with different body weight, and correlated with markers of obesity, hyperglycemia, and insulin resistance. Glucose uptake and lipolysis were measured in adipocytes ex vivo following short-term exposure to dopamine, DRD1 receptor agonist (SKF81297), or DRD2 receptor agonist (bromocriptine).

RESULTS

DRD1 and DRD2 gene expression in subcutaneous adipose tissue correlated positively with clinical markers of insulin resistance (e.g. HOMA-IR, insulin, and triglycerides) and central obesity in subjects without T2D. Protein expression of DRD2 in subcutaneous adipose tissue, but not DRD1, is higher in subjects with impaired fasting glucose and T2D and correlated positively with hyperglycemia, HbA1c, and glucose AUC, independent of obesity status. DRD1 and DRD2 proteins were mainly expressed in adipocytes, compared to stromal vascular cells. Dopamine and dopaminergic agonists did not affect adipocyte glucose uptake ex vivo, but DRD1 and DRD2 agonist treatment inhibited isoproterenol-stimulated lipolysis.

CONCLUSION

The results suggest that protein expression of DRD2 in subcutaneous adipose tissue is up-regulated with hyperglycemia and T2D. Whether DRD2 protein levels contribute to T2D development or occur as a secondary compensatory mechanism needs further investigation. Additionally, dopamine receptor agonists inhibit adipocyte beta-adrenergic stimulation of lipolysis, which might contribute to the beneficial effects in lipid metabolism as observed in patients taking bromocriptine.

Role of Estrogen and Its Receptors in Adipose Tissue Glucose Metabolism in Pre- and Postmenopausal Women

CONTEXT

Reduced estrogen levels in postmenopausal women predispose them to metabolic side effects, including insulin resistance and type 2 diabetes; however, the cellular mechanisms are not well understood.

OBJECTIVE

This work aimed to study the expression of estrogen receptors in adipose tissue from pre- and postmenopausal women and the effects of estradiol (E2) on glucose uptake of adipocytes.

METHODS

Subcutaneous (SAT) and visceral adipose tissue (VAT) obtained from pre- and postmenopausal women (19-51 and 46-75 years old, respectively) were used to measure gene expression of ESR1 and ESR2. SAT tissue was incubated with E2, and glucose uptake and estrogen receptor levels were measured. Polymorphisms in ESR1 and ESR2 were addressed in public databases to identify single nucleotide polymorphisms associated with metabolic traits.

RESULTS

ESR2 expression was lower in pre- vs postmenopausal women, corresponding to lower ESR1:ESR2 gene expression ratio in postmenopausal women. In premenopausal women, the expression of ESR1 was higher in VAT than in SAT. In both pre- and postmenopausal women, ESR2 expression was lower in VAT than in SAT. In late, but not pre- or early postmenopausal women, E2 reduced glucose uptake and GLUT4 protein and increased expression of ESR2. ESR1 polymorphisms were associated with weight, body fat distribution, and total cholesterol, and ESR2 polymorphisms were associated with total cholesterol and triglyceride levels and with body fat percentage.

CONCLUSION

E2 inhibits glucose utilization in human adipocytes in late postmenopausal women. Changes in glucose utilization over time since menopause may be explained by a lower ESR1:ESR2 ratio. This can have clinical implications on the timing of estrogen treatment in postmenopausal women.

CDKN2C expression in adipose tissue is reduced in type II diabetes and central obesity: impact on adipocyte differentiation and lipid storage?

CDKN2C/p18 (Cyclin-Dependent Kinase Inhibitor 2C) is a cell growth regulator that controls cell cycle progression and has previously been associated with increased risk for type II diabetes (T2D) and reduced peripheral adipose tissue (AT) storage capacity. This study explored the role of CDKN2C in AT lipid and glucose metabolism in T2D. Expression of CDKN2C and other genes was analyzed by transcriptomics, or real-time PCR in subcutaneous AT (SAT) samples obtained from T2D and control subjects matched for sex, age and BMI and also in paired SAT and omental AT (OAT) samples. Functional studies included adipocyte glucose uptake and lipolysis rates. CRISPR/Cas9 CDKN2C gene knockdown was performed in human preadipocytes to assess adipogenesis. CDKN2C mRNA expression in SAT and OAT was reduced in T2D and obese subjects compared to controls. CDKN2C expression in SAT was inversely correlated with measures of hyperglycemia, insulin resistance and visceral adiposity and positively correlated with expression of genes in several metabolic pathways, including insulin signaling and fatty acid and carbohydrate metabolism. CDKN2C protein was mainly expressed in adipocytes compared to stromal vascular cells, and its gene and protein expression was up-regulated during adipocyte differentiation. Knockdown of CDKN2C did not affect the percentage of differentiating cells compared to wild type cultures. However, CDKN2C knockdown cultures had significantly lower expression of differentiation markers CEBPA, ADIPOQ and FASN and transiently reduced lipid accumulation per adipocyte during differentiation. Our findings suggest that adipose CDKN2C expression might be reduced as a consequence of insulin resistance and obesity, and this can further contribute to impairment of SAT lipid storage.

Excess glucocorticoid exposure contributes to adipose tissue fibrosis which involves macrophage interaction with adipose precursor cells

Chronic exposure to elevated glucocorticoid levels, as seen in patients with Cushing's syndrome, can induce adipose tissue fibrosis. Macrophages play a pivotal role in adipose tissue remodelling. We used the synthetic glucocorticoid analogue dexamethasone to address glucocorticoid effects on adipose tissue fibrosis, in particular involving macrophage to preadipocyte communication. We analysed the direct effects of dexamethasone at a supra-physiological level, 0.3 µM, on gene expression of pro-fibrotic markers in human subcutaneous adipose tissue. The effects of dexamethasone on the differentiation of human SGBS preadipocytes were assessed in the presence or absence of THP1-macrophages or macrophage-conditioned medium. We measured the expression of different pro-fibrotic factors, including α-smooth muscle actin gene (ACTA2) and protein (α-SMA). Dexamethasone increased the expression of pro-fibrotic genes, e.g. CTGF, COL6A3, FN1, in adipose tissue. Macrophages abolished preadipocyte differentiation and increased the expression of the ACTA2 gene and α-SMA protein in preadipocytes after differentiation. Exposure to dexamethasone during differentiation reduced adipogenesis in preadipocytes, and elevated the expression of pro-fibrotic genes. Moreover, dexamethasone added together with macrophages further increased ACTA2 and α-SMA expression in preadipocytes, making them more myofibroblast-like. Cells differentiated in the presence of conditioned media from macrophages pretreated with or without dexamethasone had a higher expression of profibrotic genes compared to control cells. Our data suggest that macrophages promote adipose tissue fibrosis by directly interfering with preadipocyte differentiation and stimulating gene expression of pro-fibrotic factors. Excess glucocorticoid exposure also has pro-fibrotic effect on adipose tissue, but this requires the presence of macrophages.

A registry-based randomised trial comparing an SGLT2 inhibitor and metformin as standard treatment of early stage type 2 diabetes (SMARTEST): Rationale, design and protocol

AIM

SGLT2 inhibitors have been shown to reduce cardiovascular and renal complications in type 2 diabetes (T2D) patients at high cardiovascular risk. Metformin is currently widely used as initial monotherapy in T2D but lacks convincing data to show that it reduces risk of complications. We aim to compare the SGLT2 inhibitor dapagliflozin and metformin as first-line T2D medication with regard to development of complications in a registry-based randomised controlled trial.

METHODS

The SGLT2 inhibitor or metformin as standard treatment of early stage type 2 diabetes (SMARTEST) trial will enrol 4300 subjects at 30-40 study sites in Sweden who will be randomised 1:1 to either metformin or dapagliflozin. Participants must have T2D duration <4 years, no prior cardiovascular disease, and be either drug-naïve or on monotherapy for T2D.

RESULTS

The primary endpoint is a composite of all-cause death, major adverse cardiovascular events and occurrence or progression of microvascular complications (retinopathy, nephropathy, diabetic foot lesions). Secondary endpoints include individual components of the primary endpoint, start of insulin therapy, risk factor biomarkers, patient-reported outcome measures, and cost-effectiveness analysis. Outcomes will primarily be assessed using nationwide healthcare registries.

CONCLUSIONS

The SMARTEST trial will investigate whether dapagliflozin is superior to metformin in preventing complications in early stage T2D. (Clinicaltrials.gov identifier NCT03982381, EudraCT 2019-001046-17).

Metformin as an anti-inflammatory agent: a short review

Metformin is a biguanide drug widely used as the initial treatment of type 2 diabetes. Despite its widespread use, its precise mechanisms of action remain incompletely characterised. Its effect in lowering blood glucose is largely related to the suppression of gluconeogenesis in the liver, which is probably accomplished by partial inhibition of the mitochondrial respiratory chain complex 1 with a subsequent increase in intracellular AMP levels and activation of AMP kinase. Several local and systemic anti-inflammatory effects of metformin have been described. Many of these effects seem to be mediated by AMP kinase activation and downstream effects inhibiting mTOR and NF-κB pro-inflammatory signalling cascades. However, there are also studies describing actions independent of AMP kinase action. In this review, we summarise the currently known mechanisms of metformin on inflammatory pathways and the clinical evidence underpinning the use of metformin as a potential anti-inflammatory drug.

Impaired HMG-CoA Reductase Activity Caused by Genetic Variants or Statin Exposure: Impact on Human Adipose Tissue, β-Cells and Metabolome

Inhibition of 3-hydroxy-3-methyl-glutaryl-CoA (HMG-CoA) reductase is associated with an increased risk of new-onset type 2 diabetes. We studied the association of genetic or pharmacological HMG-CoA reductase inhibition with plasma and adipose tissue (AT) metabolome and AT metabolic pathways. We also investigated the effects of statin-mediated pharmacological inhibition of HMG-CoA reductase on systemic insulin sensitivity by measuring the HOMA-IR index in subjects with or without statin therapy. The direct effects of simvastatin (20-250 nM) or its active metabolite simvastatin hydroxy acid (SA) (8-30 nM) were investigated on human adipocyte glucose uptake, lipolysis, and differentiation and pancreatic insulin secretion. We observed that the LDL-lowering HMGCR rs12916-T allele was negatively associated with plasma phosphatidylcholines and sphingomyelins, and HMGCR expression in AT was correlated with various metabolic and mitochondrial pathways. Clinical data showed that statin treatment was associated with HOMA-IR index after adjustment for age, sex, BMI, HbA1c, LDL-c levels, and diabetes status in the subjects. Supra-therapeutic concentrations of simvastatin reduced glucose uptake in adipocytes and normalized fatty acid-induced insulin hypersecretion from β-cells. Our data suggest that inhibition of HMG-CoA reductase is associated with insulin resistance. However, statins have a very mild direct effect on AT and pancreas, hence, other tissues as the liver or muscle appear to be of greater importance.

Cardiovascular and Renal Disease Burden in Type 1 Compared With Type 2 Diabetes: A Two-Country Nationwide Observational Study

OBJECTIVE

Type 1 diabetes (T1D) and type 2 diabetes (T2D) increase risks of cardiovascular (CV) and renal disease (CVRD) compared with diabetes-free populations. Direct comparisons between T1D and T2D are scarce. We examined this by pooling full-population cohorts in Sweden and Norway.

RESEARCH DESIGN AND METHODS

A total of 59,331 patients with T1D and 484,241 patients with T2D, aged 18-84 years, were followed over a mean period of 2.6 years from 31 December 2013. Patients were identified in nationwide prescribed drug and hospital registries in Norway and Sweden. Prevalence and event rates of myocardial infarction (MI), heart failure (HF), stroke, chronic kidney disease (CKD), all-cause death, and CV death were assessed following age stratification in 5-year intervals. Cox regression analyses were used to estimate risk.

RESULTS

The prevalence of CV disease was similar in T1D and T2D across age strata, whereas CKD was more common in T1D. Age-adjusted event rates comparing T1D versus T2D showed that HF risk was increased between ages 65 and 79 years, MI between 55 and 79 years, and stroke between 40 and 54 years (1.3-1.4-fold, 1.3-1.8-fold, and 1.4-1.7-fold, respectively). CKD risk was 1.4-3.0-fold higher in T1D at all ages. The all-cause death risk was 1.2-1.5-fold higher in T1D at age >50 years, with a similar trend for CV death.

CONCLUSIONS

Adult patients with T1D compared with those with T2D had an overall greater risk of cardiorenal disease (HF and CKD) across ages, MI and all-cause death at middle-older ages, and stroke at younger ages. The total age-adjusted CVRD burden and risks were greater among patients with T1D compared with those with T2D, highlighting their need for improved prevention strategies.

Cardiac Arrest after a Transatlantic Flight in a Patient with a Large Left Atrial Myxoma

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Cardiac myxoma is the most common benign primary cardiac tumor.

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Cardiac myxomas can cause a variety of symptoms from dyspnea to cardiac arrest.

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Echocardiography plays an essential role in the diagnosis of cardiac myxomas.

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Prompt surgical excision is the gold standard treatment of cardiac myxomas.

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Air-travel predispose for cardiac decompensation in several heart conditions.

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We describe a case of cardiac decompensation in a patient with a cardiac myxoma.